A. Field of the Invention
The present invention relates to portable ladders of the type used in construction and maintenance. More particularly, the invention relates to a safety support apparatus for supporting and stabilizing the lower end of a ladder against both lateral and fore and aft motions.
B. Description of Background Art
Straight ladders consisting of either a single ladder or one or more such ladders slidably joined to one another to form an extension ladder, are widely used for maintenance and construction tasks, as well as by fire departments and emergency services. Ladders of this type typically have a pair of longitudinally elongated side rails, and a plurality of transversely disposed steps or rungs.
Straight ladders are most often used by placing the lower ends or feet of the rails on a relatively flat surface such as the ground or a floor, and leaning the upper end of the ladder against the side of a building wall, roof, tree, or other stable structure. The inclination angle of the ladder with respect to a horizontal floor or ground surface must be rather closely controlled to ensure stability of the ladder. Thus, if a ladder is inclined at too shallow an angle with respect to a horizontal surface, the rearward horizontal component of force exerted by the feet on the supporting surface in reaction to the weight of a person on the ladder may become large enough to cause the feet to slip rearward on the surface, away from the supporting wall. Conversely, if the ladder inclination angle is too large, i.e., close to 90 degrees, orienting the ladder nearly vertically, the ladder will tend to tilt backwards or even fall away from a building wall when climbed. For the foregoing reasons, ladder manufacturers typically recommend that the inclination angle be close to 75.5 degrees, corresponding to a one-foot spacing between a structure wall and the base of a ladder for each four feet of the ladder's slant length.
Some ladders are provided with "shoes" provided with a non-slip lower surface, the shoes being fixed or pivotably attached to the bottom ends of the ladder rails. Even when provided with such non-slip shoes, straight ladders are still practically restricted to a safe, stable inclination angle of about 75 degrees.
A number of U.S. patents disclose devices intended to stabilize ladders. These include:
Hurwitz, U.S. Pat. No. 3,937,298, Feb. 10, 1978, Leveling Attachment For Ladders, which discloses a leveling attachment for extension ladders which accommodates to uneven terrain and supports the ladder against leaning or tipping laterally. The attachment includes a pair of open end sockets attached at opposite ends of a transverse member which is attached to the rails of an extension ladder by a pair of laterally opposed U-bolts. Each U-bolt fits over transverse member and is bolted to a pair of longitudinally disposed channels that are attached to fore and aft sides of each longitudinal side rail of a ladder. Two short independently adjustable support legs are recessed in sockets, outboard of the ladder rails. A latching element associated with each socket locks each leg in a position of adjustment. PA1 Blackstone, U.S. Pat. No. 4,069,893, Jan. 24, 1978, Ladder Stabilizer And Leveler, which discloses a ladder stabilizer and leveler support having laterally opposed, vertically disposed truncated A-frames, each A-frame having a pair of upper and lower parallel longitudinally disposed members for attachment to the rail of a ladder, and angled between front and rear members threadably supporting screw-jack like front legs, allowing independent adjustment of the length of each leg. PA1 Kiimmerlin et al., U.S. Pat. No. 4,359,138, Nov. 16, 1982, Supporting Device For Ladders:, which discloses supporting devices for ladders having legs of individually adjustable length for supporting a ladder level on uneven surfaces, each of the supporting devices being attached to an adjacent pair of ladder rungs by a pair of laterally disposed, longitudinally opposed channel members which receive the ladder rungs, and which are held in a longitudinal spaced apart position clamping the rungs by a pair of laterally opposed, longitudinal spring or clamp member. PA1 Ralston, U.S. Pat. No. 4,519,477, May 28, 1985, Ladder Stabilizing Apparatus, which discloses an adjustable ladder stabilizing apparatus that is attached to an extension ladder having hollow rungs. The device has two stabilizing elements made of aluminum which are located at different sides of the ladder. Each stabilizing element has an upper and a lower bracket which are connected together by two rigid pivotably-linked longitudinal members. The stabilizing elements are connected to each other by rods which extend through the hollow rungs of the ladder and which connect the upper and the lower brackets. The lower bracket and the lower longitudinal member are pivotably connected, and the upper bracket has a number of apertures spaced lengthwise of the ladder. By choosing the aperture to which the upper longitudinal member is connected, the attitude of each of the lower members is varied via the pivotable connection so as to lie on the surface adjacent the ladder side. PA1 Murrell, U.S. Pat. No. 4,632,220, Dec. 30, 1986, Safety Ladder, which discloses a safety ladder having two outriggers fitted to its lower section, each outrigger extending outwardly and forwardly for the purpose of enhancing the safety of the ladder in use. Each outrigger has a foot and is capable of being folded up against and parallel to the stile to which it is fitted for storage or transportation. The outriggers are lockable in any desired position by a cam and friction plate mechanism. Preferably each stile is provided with an adjustable extension leg controlled by a ratchet and pawl arrangement to facilitate use of the ladder on uneven ground. PA1 Kitson, U.S. Pat. No. 4,648,482, Mar. 10, 1987, Ladder Anchor, which discloses a ladder anchor comprising a hollow member having at least a wedge-shaped front portion provided with a closable orifice for filling the member with ballast such as water, or discharging ballast therefrom, the member having a ground engaging surface and a top surface, the top surface having therein at least one recess for receiving one or each of the longitudinal struts of a ladder and providing a foot receiving surface between the recess or recesses and the base of the member. PA1 Cervantes, Sr., U.S. Pat. No. 4,679,652, Jul. 14, 1987, Automatically Adjustable Ladder Support, which discloses an automatically adjustable ladder support having four circular pedestals, each provided at the upper end thereof with a ball-and-socket type universal joint, the lower surface of the pedestals providing frictional engagement with the ground plane, thereby accommodating irregular ground surfaces. A pair of spring-loaded jaws extend parallel to one another for receiving the lower end of the ladder, and which, due to the weight of the ladder, are levered against a resistant spring force causing the jaws to close on the end of the ladder and secure it by clamping engagement. The jaws are mounted on end plates which are, in turn, pivotably mounted onto end wall assemblies that can rotate, thereby providing a self-adjustment of the lower end of the ladder between the jaws. PA1 Harvey et al., U.S. Pat. No. 4,798,263, Jan. 17, 1989, Ladder Stabilizer, which discloses a stabilizer device for attachment to a ladder, comprising an attachment portion adapted to be attached to a stile of a ladder and a leg portion connected to and extending away from the attachment portion, the attachment portion being provided with two projections of adjustable length extending outwardly therefrom and positioned such that the stile can pass freely therebetween, and such that the projections engage the respective edge faces of the stile when the device is rotated about an axis generally parallel to the rungs of the ladder. The device can be in the form of a ladder anchor for preventing the bottom of the ladder from slipping, or in the form of a ladder stay for holding the top of the ladder away from a wall. PA1 Warnelov, U.S. Pat. No. 4,896,745, Jan. 30, 1990, Adjustable Base For Ladders And Like Objects, which discloses an adjustable ladder base assembly for compensating an uneven foundation surface and/or to enable a ladder to be inclined at a given angle. The base assembly includes an arcuate bottom structure having footplate devices which can be brought into contact with the foundation surface, a strut which connects the two sides of the arcuate structure, and an attachment structure which is pivotally mounted to the strut and to the arcuate part and which is intended to support the ladder in a raised position. The attachment structure includes an upper, transverse bar which supports holding means for securing the sidepieces of the ladder. The bar is firmly connected by a spacer means, with a lower, transversely extending and upwardly open channel section which is intended to receive a rung of the ladder. The spacer means can be clamped to the arcuate part by the friction locking action of an upper, transversely extending U-shaped strut which embraces the arcuate part and is pivotally mounted to the strut via a lower arm. PA1 Worthington, Jr., U.S. Pat. No. 5,044,468, Sep. 3, 1991, Ladder Leveling Device, which discloses a ladder leveling device having a pair of hydraulic cylinder/piston units to be secured at the outside lower ends of the ladder side rails in a manner so that the piston rods of the units extend as ladder supports. The working chambers of the units are in fluid communication with each other through a valved passageway which, when open, allow both piston rods to adapt to an irregular supporting surface while the ladder is oriented in a vertical plane. Upon closure of the passageway to isolate the working chambers of the respective units, the piston rods act as rigid extensions of the ladder side rails. Valving of the passageway is effected by an actuating member extending between the side rails in the region of a lower ladder rung so that the member may be depressed to close the passageway by one ascending the ladder by simply stepping on the actuating member.
None of the patents cited above discloses a ladder support apparatus which permits the ladder to be safely used at angles which deviate significantly from the recommended angle of about 75 degrees. The present invention was conceived of to provide a safety support apparatus for ladders which allows a ladder to be safely used over a relatively wide range of inclination angles, and which overcomes certain other limitations of prior art ladder support devices.